Improve output of `genErrors`

- [ ] `genErrors` always generates fully qualified names. The output would be a lot more readable if we postprocess the string to remove those qualifiers.
- [ ] We could also give a number that indicates which failure happened, for easier identification.
- [ ] The output generates non-breaking spaces. We may want to replace them with regular spaces (but maybe that should be a downstream responsibility?)

Locate the genErrors generator and inspect the output it produces, using the three checklist items as the starting scope. Compare the current work with merged pull request #551 before proceeding; the desired handling of qualified names, failure numbers, and non-breaking spaces is not fully settled in the issue.

Written by the indexing model from the issue text.